Information recording medium

ABSTRACT

In an information recording medium comprising at least a substrate, a recording layer, and a resin layer, the substrate is formed with at least a pit corresponding to a read only area  31  and a groove corresponding to a recording/reproducing area  32  without overlapping with each other. A reflectivity of the recording layer is specified to be more than 10%. The recording layer and the resin layer are continuously adhered over both the read only and recording/reproducing areas  31  and  32 . The information recording medium is characterized in that both push-pull signal outputs T 1  and T 2 , which are reproduced from the read only area  31  and the recording/reproducing area  32  respectively, are more than 0.1 and satisfy an inequality 1.5≧T 1 /T 2 ≧0.5.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an information recording mediumutilized for an optical recording/reproducing apparatus, which reads outinformation recorded on the information recording medium by making theinformation recording medium relatively move, particularly, relates toan information recording medium comprising a read only area of enablingto read out information and a recording/reproducing area of enabling torecord and reproduce information.

2. Description of the Related Art

Currently various types of information recording mediums such as in adisk shape, in a card shape, and in a tape shape are utilized as anoptical information recording medium from which information is read outby making the information recording medium relatively move. Suchinformation recording mediums are divided into two types inconsideration of mechanism of recording or reproducing: one is a readonly type and the other is a recording/reproducing type, that is, arecordable type and an overwritable type. A read only type informationrecording medium is shipped out into a market with being prerecordedwith information such as a CD audio disk typically, and is reproduced bya user. On the other hand, a recordable or overwritable type informationrecording medium is shipped out into a market without any recordedinformation, and a user records information on it and reproduces it ifnecessary.

A problem arises along with a trend toward multimedia causing toincrease a chance such that copyright is infringed by using anelectronic means. Accordingly, in order to prevent such the problem, anidea such as embedding a specific code, which can not be rewritten by auser, is necessary to be realized even in a recordable or overwritabletype information recording medium, which can be recorded freely by auser.

As mentioned above, various kinds of information recording mediums,which are provided with two areas composed of a read only area and arecording/reproducing area, have been introduced. For example, there isexisted an information recording medium provided with arecording/reproducing area only in a predetermined angle. Further,another information recording medium having a recording/reproducingarea, which is provided with a read only area allocated in each one halftrack, is introduced.

Furthermore, an information recording medium provided with both a readonly area and a recording/reproducing area, which are allocated indifferent positions from each other, is introduced. FIG. 2 is a crosssectional view of such the information recording medium 301. In FIG. 2,the information recording medium 301 comprises a substrate 10, arecording layer 13, and a resin layer 14. A microscopic pattern isformed on a surface of the substrate 10 at a boundary area between thesubstrate 10 and the recording layer 13. Microscopic patternsconstituting a read only area and a recording/reproducing area areengraved in areas corresponding to the read only andrecording/reproducing areas respectively. Actually, microscopic patterns11 corresponding to the read only area and other microscopic patterns 12corresponding to the recording/reproducing area are engraved. Thesemicroscopic patterns 11 and 12 are different from each other in depth. Adepth “d1” of the microscopic patterns 11 is λ/4n, on the other hand, adepth “d2” of the microscopic patterns 12 is λ/8n, wherein λ is areproduction wavelength of a laser beam and “n” is a refractive index ofthe substrate 10 at the reproduction wavelength λ. Specifying the depthof the microscopic patterns 11 to λ/4n is caused by a phase depth inwhich a signal output from the read only area becomes maximum. Further,specifying the depth of the microscopic patterns 12 to λ/8n is caused bythat a push-pull signal related to tracking of the information recordingmedium becomes a maximum output.

As mentioned above, allocating two areas in different positions reducesload of a recording/reproducing apparatus due to a simplified layout.Accordingly, there is much merit.

However, there is existed a following problem of the prior art mentionedabove. A defect has occurred when an information recording medium formedwith microscopic patterns shown in FIG. 2 has been loaded in variousrecording/reproducing apparatuses, which are currently available in amarket, and operated. A mode of the defect is out of tracking whilereproducing the information recording medium with continuouslytraversing from a recording/reproducing area to a read only area.Further, an operation traversing reversely from the read only area tothe recording/reproducing area is also defective. According to ourcareful investigation of the problem, it is found that arecording/reproducing apparatus employs a push-pull method for trackingso as to record information in a groove and the push-pull method doesnot match with the information recording medium 301. In other words,firstly, the problem is caused by that forming the read only area in thedepth of d1=λ/4n results a push-pull signal output in zero. In a casethat the push-pull signal output is zero, a track can not be detected.Therefore, the reproduction stops at the track. Further, as a secondproblem, output difference between a push-pull signal output of the readonly area and a push-pull signal output of the recording/reproducingarea is large, so that a servo system of the recording/reproducingapparatus can not follow properly. Accordingly, it is required to solvesuch the problem as out of tracking when an information recording mediumhaving two areas is actually recorded and reproduced.

SUMMARY OF THE INVENTION

Accordingly, in consideration of the above-mentioned problems of theprior art, an object of the present invention is to provide aninformation recording medium, which can solve the problem mentionedabove.

In order to achieve the above object, the present invention provides,according to an aspect thereof, an information recording medium, whichcomprises a substrate, a recording layer, and a resin layer, wherein thesubstrate is formed with a pit corresponding to a read only area and agroove corresponding to a recording/reproducing area without overlappingwith each other, and wherein a reflectivity of the recording layer ismore than 10%, the information recording medium is characterized in thata push-pull signal output T1 reproduced from the read only area andanother push-pull signal output T2 reproduced from therecording/reproducing area is more than 0.1 respectively and further1.5≧T1/T2≧0.5.

Other object and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view of an information recording medium in a disk shapeaccording to an embodiment of the present invention.

FIG. 2 is a cross sectional view of an information recording mediumcommon to a prior art and the present invention.

FIG. 3 is a cross sectional view of an information recording mediumaccording to the present invention.

FIG. 4 is a cross sectional view of an information recording mediumaccording to a first embodiment of the present invention.

FIG. 5 is a plan view of a boundary area between a read only area and arecording/reproducing area of an information recording medium accordingto the present invention.

FIG. 6 is a plan view of a boundary area between a read only area and arecording/reproducing area of an information recording medium accordingto the present invention.

FIG. 7 is a plan view of a boundary area between a read only area and arecording/reproducing area of an information recording medium accordingto the present invention.

FIG. 8 is a plan view of a boundary area between a read only area and arecording/reproducing area of an information recording medium accordingto the present invention.

FIG. 9 is a cross sectional view of a 4-division photodetector utilizedfor recording and reproducing an information recording medium accordingto the present invention.

FIG. 10 is a graph showing a relation between a depth of a read onlyarea of an information recording medium and a push-pull signal outputaccording to the present invention.

FIG. 11 is a graph showing a relation between a depth of arecording/reproducing area of an information recording medium and apush-pull signal output according to the present invention.

FIG. 12 is a plan view of an information recording medium in a cardshape according to the present invention.

FIG. 13 is a plan view of another information recording medium in a cardshape according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With referring to drawings, details common to all embodiments of thepresent invention are explained first.

FIG. 1 is a plan view of an information recording medium in a disk shapeaccording to an embodiment of the present invention.

FIG. 2 is a cross sectional view of the information recording mediumshown in FIG. 1.

FIG. 3 is another cross sectional view of the information recordingmedium shown in FIG. 1.

In FIG. 1, an information recording medium 1 in a disk shape comprises aread only area 31 and a recording/reproducing area 32. As shown in FIG.1, the read only area 31 and the recording/reproducing area 32 isallocated in an innermost circumference area and an outer circumferencearea of the information recording medium 1 respectively. However, theseallocations can be reversely arranged. Further, these two areas areformed not so as to overlap with each other. Some gap existing betweentwo areas can be allowable. Furthermore, a plurality of the read onlyand recording/reproducing areas 31 and 32 can also be allowable.

FIG. 2 shows a fundamental configuration of an information recordingmedium 1 of the present invention. The information recording medium 1 ofthe present invention is resemble to that of the prior art inappearance, so that the same drawing is used for explaining the presentinvention. FIG. 3 also shows a fundamental configuration of aninformation recording medium 2 of the present invention. Theconfiguration shown in FIG. 3 is a same as that shown in FIG. 2 except areading out direction, that is, an optical path. An optical path will beexplained.

As shown in FIGS. 2 and 3, the information recording medium 1 or 2comprises a substrate 10, a recording layer 13 and a resin layer 14. Amicroscopic pattern is formed on a surface of the substrate 10 at aboundary between the substrate 10 and the recording layer 13.Microscopic patterns 11 and 12 are formed in areas corresponding to theread only area 31 and the recording/reproducing area 32 respectivelywithout overlapping with each other.

Further, these microscopic patterns 11 and 12 have a depth of “d1” and“d2” respectively. Either cases can be acceptable whether or not thedepth “d1” of the microscopic patterns 11 is a same as the depth “d2” ofthe microscopic patterns 12. However, a depth must be designated so asto be able to obtain a range of push-pull signal output, which will bedepicted.

Layers composed of the substrate 10, the recording layer 13, and theresin layer 14 are formed in parallel to each other. The resin layer 14is adhered on the recording layer 13 with continuously covering over allareas including at least the read only area 31 and therecording/reproducing area 32. Although recording or reproducing bylight beam is performed on the recording layer 13, it is arbitrarilydetermined that a laser beam having a wavelength of λ nm, which isstopped down by a objective lens having a numerical aperture of NA, isirradiated from either side of the information recording medium 1. Inother words, it is arbitrarily determined whether the laser beam isirradiated from the substrate 10 side or the resin layer 14 side.Further, a path of irradiating the laser beam, that is, an optical pathhas a certain refractive index “n” for the wavelength λ. An effectiveoptical length is determined by the refractive index “n”. The substrate10 is illustrated as an optical path in FIG. 2. However, the resin layer14 can be used as an optical path as shown in FIG. 3. The refractiveindex “n” of these optical paths is desirable to be 1.4 through 1.7 inconsideration of interchangeability with current optical disks, moredesirable to be 1.45 through 1.65. Further, if birefringence of theoptical path is designated to be less than 100 nm by double paths,deviation of reproduction output can be sufficiently suppressed, so thatit is most desirable.

Synthetic resins of high strength and various ceramics can be utilizedfor a material of the substrate 10. Actual materials are such resins aspolycarbonate, polymethyl methacrylate, polystyrene,polycarbonate-polystyrene copolymer, polyvinyl chloride, alicyclicpolyorefin, polymethyl pentene, polyacetate resin, and various copolymerhaving a resin frame of them, and such synthetic resin as block polymer,and such ceramics as soda aluminosilicate glass, boron silicate glass,and silica glass.

Further, the recording layer 13 is at least made of a recording materialof which a reflectivity is more than 10% at the wavelength λ. Actually,following materials can be used for a recording material of enablingrecordable or write once recording: such dye materials as cyanine dye,phthalocyanine dye, naphthalocyanine dye, azo dye, and naphthoquinonedye. Furthermore, a phase change recording material, so called, and amagneto-optical recording material can be used for a recording materialof enabling overwrite. Typical phase change recording materials are asfollows: alloys made of some materials selected from indium, antimony,tellurium, selenium, germanium, gallium, bismuth, platinum, gold,silver, copper, tin, sulfur, and aluminum, wherein an alloy includescompound such as oxide, nitride, and carbide. Moreover, in a case ofmagneto-optical recording material, there existed an alloy, whichcontains at least a transition metal and a rare earth element. The alloyis made of some materials selected from terbium, cobalt, iron,gadolinium, neodymium, dysprosium, bismuth, palladium, samarium,holmium, praseodymium, manganese, titanium, erbium, ytterbium, lutetium,chromium, tin, platinum, wherein an alloy includes compound such asoxide, nitride, and carbide. In addition thereto, the recording layer 13can be multi-layered or laminated by an optical interference film suchas SiN, SiC, SiO, ZnS, ZnSSiO, AlO, GeN, MgF, InO, and ZrO, and anoptical reflection film such as aluminum, gold, silver, and titanium fora purpose of improving performance. In order to perform high densityrecording and reproducing, the recording layer 13 can be laminated by asuper resolution masking film or a contrast enhancing film, which iscommonly known.

The resin layer 14 is provided for protecting the recording layer 13chemically and physically, and can be selected from thermosettingresins, ultra violet ray curable resins, various radiation includingvisible light curable resins, electron beam curable resins, moisturecurable resins, and multiple liquid mixture curable resins. A surface ofthe resin layer 14 can be printed if necessary.

FIG. 5 is a plan view of a boundary area between a read only area and arecording/reproducing area of an information recording medium partiallyenlarged according to the present invention. There existed a gap havinga distance of “G” (hereinafter referred to a gap “G”) between the readonly area 31 and the recording/reproducing area 32 caused by amanufacturing process of the information recording medium 1. In otherwords, as shown in FIG. 5, the gap “G” exists between the microscopicpatterns 11 of the read only area 31 and the microscopic patterns 12 ofthe recording/reproducing area 32. Basically, a recording/reproducingapparatus can jump across the gap “G” by forcing to drive a pickup or alike. According to our experiment, the jumping motion can be smoothlyperformed by setting the gap “G” in less than 25 μm.

As shown in FIG. 5, the microscopic patterns 11 of the read only area 31is a group of pit 21, which is engraved by what is called a recordingmethod of cutting. A track is composed of continuing groups of the pit21. The microscopic patterns 12 utilized for the recording/reproducingarea 32 are not formed in the read only area 31. A gap between eachtrack is in a distance of P1 (hereinafter referred to a track pitch P1).The pit 21 is modulated by a well-known modulation method and formed apit in various length. A minimal pit length closely relating to qualityof a reproduction signal is defined as L1. The groups of pit 21 can bemeandered or wobbled by applying a sinusoidal deflection to the pit 21when the pit 21 is recorded with cutting. It is acceptable that wobblingis recorded by either the CLV (constant linear velocity) or the CAV(constant angular velocity) method. Further, a specific code, which cannot be rewritten by a user, is recorded in the read only area 31. Thespecific code is such a key or code as a key for ciphering, a key fordeciphering, a code for permitting to record, a code for refusing torecord, and a disk serial number inherent to each disk. In additionthereto, a lead-in signal can be recorded as a same manner as that of acurrent read only disk.

The microscopic patterns 12 in the recording/reproducing area 32 arecomposed of a group of groove 22. A gap between each groove 22 is calleda land 23 commonly. Each groove 22 is spaced in a distance of P2(hereinafter referred to a track pitch P2). The groove 22 can also bewobbled by applying a sinusoidal deflection to the groove 22 when thegroove 22 is recorded with cutting. It is acceptable that wobbling isrecorded by either the CLV or the CAV method. Further, an address pit,which specifies an address number, can be allocated in between eachgroove 22, that is, in the land 23.

Recording an information by a user is explained next.

FIG. 6 is a plan view of the interface area as same as that of shown inFIG. 5 with showing a mark 24 written in the groove 22.

FIG. 7 is a plan view of the interface area as same as that of shown inFIG. 5 with showing the mark 24 written in the land 23.

Recording is performed as shown in FIG. 6. That is to say, the mark 24is formed in the groove 22 by focusing a laser beam for recording on thegroove 22. The mark 24 is modulated by a well-known modulating method,and then formed in various lengths. A minimal pit length closelyrelating to quality of a reproduction signal is defined as L2. As shownin FIG. 7, the mark 24 can be written in between each groove 22, thatis, in the land 23. Further, the mark 24 can be written in both thegroove 22 and the land 23 although not shown in any drawings.

The well-known modulation method applied for the read only andrecording/reproducing areas 31 and 32 is a signal of which minimal marklength is specified to one of lengths such as 2T, 3T, 4T, and 5T. In acase of a signal system in which a minimal pit length or a minimal marklength is specified to 2T, for example, such a signal system as an eightto twelve (8/12) modulation, which is composed of signals from 2T to 8T,can be utilized. Further, in a case of a signal system in which aminimal pit length or a minimal mark length is specified to 3T, signalsystems such as an eight to fourteen (8/14) modulation, an eight tofifteen (8/15) modulation, and an eight to seventeen (8/17) modulation,which are composed of signals from 3T to 11T, and another signal systemsuch as an eight to sixteen (8/16) modulation, which is composed ofsignal from 3T to 11T and 14T, can be utilized. In these read only andrecording/reproducing areas 31 and 32, each signal in the respectiveareas can be modulated by different modification methods. However, asame modification method is desirable to be employed, in considerationof convenience of a recording/reproducing apparatus. It is alsodesirable by the same reason that P1=P2 and L1=L2.

In order to enable a traverse reproduction over the read only area 31and the recording/reproducing area 32, the depth d1 and d2 of respectiveareas of the information recording medium 1 according to the presentinvention are adjusted so as to enable to obtain a predeterminedpush-pull signal. A predetermined push-pull signal satisfies followinginequalities simultaneously with defining that a push-pull signal outputof the read only area 31 is T1 and a push-pull signal output of therecording/reproducing area 32 before recording is T2.T1≧0.1T2≧0.1 and1.5≧T1/T2≧0.5.Further, in order to stabilize a traverse reproduction over areas,respective push-pull signal outputs are desirable to be within a rangeof satisfying following inequalities simultaneously:T1≧0.15T2≧0.15 and1.4≧T1/T2≧0.6.

A range of tracking signal of the information recording medium accordingto the present invention is obtained by a limiting value, which isobtained by reproducing the information recording medium actually loadedin a player by means of the push-pull method. A result of experiment isshown in Table 1. By examining tracking ability in the read only area 31with respect to T1, tracking is completely disabled by T1 in less than0.08. TABLE 1 T1 Tracking 0.08 Disable 0.10 Enable 0.15 Enable 0.18Enable 0.25 Enable

Further, Table 2 shows a result of examining tracking ability in therecording/reproducing area 31 with respect to T2. Tracking is completelydisabled by T2 in less than 0.08 as same situation as that of T1. TABLE1 T2 Tracking 0.08 Disable 0.10 Enable 0.15 Enable 0.22 Enable 0.31Enable 0.45 Enable

It is found by the above experiment that a value of both T1 and T2 mustbe more than 0.1. Furthermore, the value is desirable to be more than0.15, in consideration of a case that the information recording medium 1is dusted or scratched.

A limitation of continuous reproducibility over two areas is caused bythat there is existed a limit in a dynamic range of a servo circuit of arecording apparatus. In other words, it is required that a differencebetween T1 and T2 is smaller. Therefore, with respect to the informationrecording medium 1, which satisfies the inequalities of T1≧0.1 andT2≧0.1, a limiting value is obtained by performing a traversereproduction over two areas for various disk samples of T1/T2. A resultis shown in Table 3 below. As shown in Table 3, the traversereproduction over two areas is enabled in a case that T1/T2 is within arange from 0.5 to 1.5. However, the value is desirable to be within arange from 0.6 to 1.4, in consideration of a case that the informationrecording medium 1 is dusted or scratched. TABLE 3 T1 T2 T1/T2 Traversereproduction over areas 0.10 0.10 1.0 Enable 0.10 0.20 0.5 Enable 0.100.25 0.4 Disable 0.15 0.22 0.7 Enable 0.20 0.12 1.7 Disable 0.20 0.131.5 Enable 0.20 0.28 0.7 Enable 0.20 0.40 0.5 Enable 0.20 0.45 0.4Disable 0.22 0.16 1.4 Enable 0.25 0.16 1.6 Disable 0.25 0.17 1.5 Enable0.25 0.25 1.0 Enable 0.25 0.34 0.7 Enable 0.25 0.44 0.6 Enable

A push-pull signal output is defined as follows: a push-pull signal is asignal, which is produced by calculating respective outputs from a4-division photodetector utilized for a recording/reproducing apparatusas a pickup.

FIG. 9 is a cross sectional view of a 4-division photodetector 9utilized for recording and reproducing the information recording medium1 according to the present invention.

In FIG. 9, a horizontal and vertical axes are a radial direction and atangential direction (track direction) respectively in corresponding toFIGS. 5 through 7. Reproduced outputs of the 4-division photodetector 9are Ia, Ib, Ic, and Id respectively. An output difference between aninner circumference side and an outer circumference side, that is,|(Ia+Ib)−(Ic+Id)| is measured by an AC (alternative current) coupling,and then total outputs, that is, |(Ia+Ib+Ic+Id)| is measured by a DC(direct current) coupling. A push-pull signal “T” is a ratio of thesetwo values and defined as follows:T=|(Ia+Ib)−(Ic+Id)|/|(Ia+Ib+Ic+Id)|.

As mentioned above, in the information recording medium 1 having atleast the read only and recording/reproducing areas 31 and 32, in orderto enable the traverse reproduction over two areas, the presentinvention specifies a push-pull signal output to a predetermined range.

First Embodiment

FIG. 1 is a plan view of an information recording medium in a disk shapeaccording to an embodiment of the present invention.

FIG. 4 is a cross sectional view of the information recording mediumshown in FIG. 1 according to a first embodiment of the presentinvention.

In FIG. 1, an information recording medium 3 comprises a read only area31 formed a ring shape in an inner circumference area and arecording/reproducing area 32 formed a ring shape in an area outside theread only area 31. As shown in FIG. 4, the information recording medium3 comprises a substrate 10, a recording layer 13, a resin layer 14 and adummy substrate 15. The resin layer 14 is adhered on the recording layer13 with continuously covering over two areas including the read onlyarea 31 and the recording/reproducing area 32. The substrate 13comprises polycarbonate of which a refractive index “n” is 1.58 at awavelength λ of 650 nm. The recording layer 13 comprises a phase changematerial having a reflectivity of more than 15% such as an alloy ofantimony, tellurium, and a metal having a melting point of less than1100° C. Actually, the alloy is composed of silver, indium, antimony,and tellurium (AgInSbTe), for example. The alloy is sandwiched bydielectric such as ZnSSiO and further laminated by a reflection film ofan aluminum alloy, and then they are formed as a recording layer havinga reflectivity of 18 to 30%. The resin layer 14 comprises an ultraviolet curable resin and is adhered to the dummy substrate 15 withlaminated.

FIG. 8 is a plan view of microscopic patterns 11 and 12 formed on thesubstrate 10 typically before recording information.

In FIG. 8, a gap “G” between the microscopic pattern 11 and 12, that is,a gap “G” between the read only area 31 and the recording/reproducingarea 32 is 25 μm. The microscopic patterns 11 corresponding to the readonly area 31 is recorded spirally by the CLV method, that is, a group ofpit 21, which is wobbled sinusoidally. A width of wobbling is 0.009 to0.017 μm. An average track pitch P1 of the microscopic patterns 11 is0.74 μm. With respect to a modification method of the read only area 31,the 8/16-modification method is utilized. A minimal pit length of thepit 21 is 0.4 μm.

On the other hand, the recording/reproducing area 32 is composed of asinusoidally wobbled groove 22 and an address pit 25 formed on a land23, which is provided between each groove 22 with being adjacent to agroove wall. These groove 22 and address pit 25 is also formed in aspiral. A width of wobbling is 0.009 to 0.017 μm. An average track pitchP2 of the microscopic patterns 12 is 0.74 μm. In addition thereto, theaddress pit 25 is a pit recorded with an address, which is useful whenrecording, and is recorded throughout the information recording mediumfrom an innermost circumference area to an outermost circumference areain accordance with a certain rule. Recording is performed by forming amark (not shown) in the groove 22. With respect to a recordingmodulation method of the recording/reproducing area 32, the8/16-modulation method is utilized as same as that of the read only area31. A minimal pit length L2 (not shown) of a recorded mark in the groove2 is 0.4 μm as a same length as the minimal pit length L1.

When such the information recording medium is reproduced by using apickup having a wavelength λ of 650 nm and a numerical aperture NA of0.6, in order to accomplish a range of push-pull signal output, that is,T1≧0.1, T2≧0.1, and 1.5≧T1/T2≧0.5, it is effective to optimize depths d1and d2 of the microscopic patterns 11 and 12 in the read only area 31and the recording/reproducing area 32 respectively.

FIG. 10 is a graph showing a relation between the depth d1 of the readonly area 31 of the information recording medium and a push-pull signaloutput T1 according to the present invention. A vertical and horizontalaxes represent a value of (d1×n) divided by λ, that is, (nd1/λ) and apush-pull signal output T1 respectively. The T1 is defined by the sinefunction of the P1. According to FIG. 10, the (nd1/λ) is specified to0.03 through 0.22 so as to realize T1≧0.1. Further, a reproductionjitter, which is fluctuation in a time axis direction, decreases as faras the (nd1/λ) approaches to 0.25, so that it is proper for the (nd1/λ)to be 0.12 through 0.22 in a depth.

FIG. 11 is a graph showing a relation between the depth d2 of therecording/reproducing area 32 of the information recording medium and apush-pull signal output T2 according to the present invention. The T2 isdefined by the sine function of the P2 as same as the T1. However, in acase of a groove, a value of the T2 is approximately twice a value ofthe T1. According to FIG. 11, the (nd2/λ) is specified to 0.02 through0.23 so as to realize T2≧0.1. Further, when the information recordingmedium is recorded and reproduced, a jitter decreases in conjunctionwith reflectivity, which increase, as far as the (nd2/λ) approaches tozero, so that it is proper for the (nd2/λ) to be 0.02 through 0.12 in adepth.

Furthermore, a reproduction jitter can be obtained in accordance withthe Annex “F” of JIS-X-6241 (Japanese Industrial Standard). According tothe Standard, a jitter is required to be not more than 8%. In otherwords, if a jitter exceeds 8%, reading out a reproduction signal isseriously affected by disturbance such as disk tilt. By recording andreproducing practically, and by optimizing the depths d1 and d2, rangesof (nd1/λ) and (nd2/λ) are as follows:

(nd1/λ) is within a range from 0.17 to 0.22, wherein the T1 is 0.1through 0.22, and

(nd2/λ) is within a range from 0.02 to 0.10 wherein the T2 is 0.1through 0.42.

With referring to FIGS. 10 and 11, (nd1/λ) and (nd2/λ) can be selectedout from the ranges shown above so as for the T1/T2 to be 0.5 through1.5. It is specified that (nd1/λ)=0.17 and (nd2/λ)=0.06 in thisembodiment. In this case, T1=0.22 and T2=0.31, and then it is obtainedthat T1/T2=0.7. Accordingly, the push-pull conditions of the presentinvention such that T1≧0.1, T2≧0.1, and 1.5≧=T1/T2≧0.5 can besufficiently satisfied. Further, reproduction jitter in the read onlyarea 31 and the recording/reproducing area 32 are 7.9% and 6.2%respectively. Both jitter values sufficiently satisfy the standard.Furthermore, by continuously reproducing two areas, it is confirmed thata continuous reproduction can jump across the two areas without anyproblems.

Second Embodiment

Parameters of this embodiment are a same as those of the firstembodiment except for (nd1/λ)=0.18 and (nd2/λ)=0.08. Further, the gap“G” between the read only area 31 and the recording/reproducing area 32are specified to 20 μm. By these parameters, it is obtained that T1=0.19and T2=0.37, and then T1/T2=0.5 is obtained. Accordingly, the push-pullconditions of the present invention such that T1≧0.1, T2≧0.1, and1.5≧T1/T2≧0.5 can be satisfied. Further, reproduction jitter in the readonly area 31 and the recording/reproducing area 32 are 7.1% and 6.5%respectively. Both jitter values sufficiently satisfy the standard.Furthermore, by continuously reproducing two areas, it is confirmed thata continuous reproduction can jump across the two areas without anyproblems.

Third Embodiment

Parameters of this embodiment are a same as those of the firstembodiment except for (nd2/λ)=0.175 and (nd2/λ)=0.067. Further, the gap“G” between the read only area 31 and the recording/reproducing area 32are assigned to 0.74 μm, which is the same value as P1 and P2. By theseparameters, it is obtained that T1=0.20 and T2=0.33, and then T1/T2=0.6is obtained. Accordingly, the push-pull conditions of the presentinvention such that T1≧0.1, T2≧0.1, and 1.5≧T1/T2≧0.5 can be satisfied.Further, reproduction jitter in the read only area 31 and therecording/reproducing area 32 are 7.5% and 6.3% respectively. Bothjitter values sufficiently satisfy the standard. Furthermore, bycontinuously reproducing two areas, it is confirmed that a continuousreproduction can be performed without stopping at a boundary between twoareas.

Fourth Embodiment

Parameters of this embodiment are a same as those of the firstembodiment except for (nd1/λ)=0.2 and (nd2/λ)=0.04. Further, the gap “G”between the read only area 31 and the recording/reproducing area 32 areassigned to 0.74 μm, which is the same value as P1 and P2. By theseparameters, it is obtained that T1=0.15 and T2=0.22, and then T1/T2=0.66is obtained. Accordingly, the push-pull conditions of the presentinvention such that T1≧0.1, T2≧0.1, and 1.5≧T1/T2≧0.5 can be satisfied.Further, reproduction jitter in the read only area 31 and therecording/reproducing area 32 are 6.8% and 5.8% respectively. Bothjitter values sufficiently satisfy the standard. Furthermore, bycontinuously reproducing two areas, it is confirmed that a continuousreproduction can be performed without stopping at a boundary between twoareas.

Fifth Embodiment

Parameters of this embodiment are a same as those of the firstembodiment except for (nd1/λ)=0.17 and (nd2/λ)=0.04. Further, the gap“G” between the read only area 31 and the recording/reproducing area 32are assigned to 0.74 μm, which is the same value as P1 and P2. By theseparameters, it is obtained that T1=0.22 and T2=0.22, and then T1/T2=1.0is obtained. Accordingly, the push-pull conditions of the presentinvention such that T1≧0.1, T2≧0.1, and 1.5≧T1/T2≧0.5 can be satisfied.Further, reproduction jitter in the read only area 31 and therecording/reproducing area 32 are 7.9% and 5.9% respectively. Bothjitter values sufficiently satisfy the standard. Furthermore, bycontinuously reproducing two areas, it is confirmed that a continuousreproduction can be performed without stopping at a boundary between twoareas.

Sixth Embodiment

Parameters of this embodiment are a same as those of the firstembodiment except for (nd1/λ)=0.17 and (nd2/λ)=0.03. Further, the gap“G” between the read only area 31 and the recording/reproducing area 32are assigned to 0.74 μm, which is the same value as P1 and P2. By theseparameters, it is obtained that T1=0.22 and T2=0.167, and then T1/T2=1.4is obtained. Accordingly, the push-pull conditions of the presentinvention such that T1≧0.1, T2≧0.1, and 1.5≧T1/T2≧0.5 can be satisfied.Further, reproduction jitter in the read only area 31 and therecording/reproducing area 32 are 7.9% and 5.5% respectively. Bothjitter values sufficiently satisfy the standard. Furthermore, bycontinuously reproducing two areas, it is confirmed that a continuousreproduction can be performed without stopping at a boundary between twoareas.

Seventh Embodiment

Parameters of this embodiment are a same as those of the firstembodiment except for (nd1/λ)=0.17 and (nd2/λ)=0.028. Further, the gap“G” between the read only area 31 and the recording/reproducing area 32are assigned to 0.74 μm, which is the same value as P1 and P2. By theseparameters, it is obtained that T1=0.25 and T2=0.158, and then T1/T2=1.5is obtained. Accordingly, the push-pull conditions of the presentinvention such that T1≧0.1, T2≧0.1, and 1.5≧T1/T2≧0.5 can be satisfied.Further, reproduction jitter in the read only area 31 and therecording/reproducing area 32 are 7.9% and 5.4% respectively. Bothjitter values sufficiently satisfy the standard. Furthermore, bycontinuously reproducing two areas, it is confirmed that a continuousreproduction can be performed without stopping at a boundary between twoareas.

Eighth Embodiment

An embodiment of the information recording medium, which is recorded orreproduced by using a blue semiconductor laser beam having a wavelengthλ of 405 nm is explained next as an expanded embodiment of the presentinvention. An information recording medium 2 has a cross sectionalconfiguration shown in FIG. 3. The information recording medium 2comprises a substrate 10 composed of polycarbonate, a recording layer 13composed of a phase change material having reflectivity of more than10%, particularly, an alloy composed of antimony, tellurium, and a metalhaving a melting point of less than 1100° C., and a resin layer 14.Further, the recording layer 13 actually comprises an alloy composed ofsilver, indium, antimony, and tellurium (AgInSbTe), for example. Thealloy is sandwiched by dielectric such as ZnSSiO and further laminatedby a reflection film of an aluminum alloy, and then they are formed as arecording layer having a reflectivity of 10 to 25%. The resin layer 14comprises polycarbonate having a refractive index “n” of 1.6 at thewavelength λ of 405 nm.

Microscopic patterns on a surface of the substrate 10 in both the readonly area 31 and the recording/reproducing area 32 are recorded spirallyby the CAV method with being wobbled sinusoidally. Other parameters arethe same as those of the first embodiment except for an average trackpitch such that P1 and P2 is 0.374 μm, wherein respective width ofwobbling is 0.006 to 0.011 μm. With respect to a modification method,the D8/15-modification method, which is one variation of the8/15-modulation method and disclosed in the Japanese Patent ApplicationNo 11-23316/1999, is utilized. A minimal pit length L1 and a minimalmark length L2 is 0.2 μm respectively.

Parameters in the read only and recording/reproducing areas 31 and 32are specified to (nd1/λ)=0.18 and (nd2/λ)=0.08 respectively. Further,the gap “G” between the read only area 31 and the recording/reproducingarea 32 are specified to 0.374 μm, which is the same value as P1 and P2.By these parameters, it is obtained that T1=0.19 and T2=0.38, and thenT1/T2=0.5 is obtained. Accordingly, the push-pull conditions of thepresent invention such that T1≧0.1, T2≧0.1, and 1.5≧T1/T2≧0.5 can besatisfied. Further, by continuously reproducing two areas, it isconfirmed that a continuous reproduction can jump across the two areaswithout any problems.

Ninth Embodiment

Parameters of this embodiment are a same as those of the seventhembodiment except for (nd1/λ)=0.17 and (nd2/λ)=0.028. Further, the gap“G” between the read only area 31 and the recording/reproducing area 32are assigned to 0.374 μm, which is the same value as P1 and P2. By theseparameters, it is obtained that T1=0.26 and T2=0.17, and then T1/T2=1.5is obtained. Accordingly, the push-pull conditions of the presentinvention such that T1≧0.1, T2≧0.1, and 1.5≧T1/T2≧0.5 can be satisfied.Further, by continuously reproducing two areas, it is confirmed that acontinuous reproduction can be performed without stopping at a boundarybetween two areas.

While the invention has been described above with reference to specificembodiments thereof, it is apparent that many changes, modifications andvariations in the arrangement of equipment and devices and in materialscan be made without departing from the invention concept disclosedherein.

FIG. 12 is a plan view of an information recording medium in a cardshape according to the present invention.

FIG. 13 is a plan view of another information recording medium in a cardshape according to the present invention.

Each composing element in some embodiments shown by drawings can beinterchanged or replaced by other composing element described in thespecification. For example, in the first and second embodiments, theinformation recording medium is exemplified by a disk shaped one.However, as shown in FIG. 12, an information recording medium 101 in acard shape provided with a read only area 131 in a stripe and arecording/reproducing area 132 in a stripe can be utilized. Further, asshown in FIG. 13, an information recording medium 201 in a card shapeprovided with a read only area 231 in a ring shape and arecording/reproducing area 232 in a ring shape can also be utilized.

Furthermore, in the first and second embodiments, a phase changerecording material is utilized for the recording layer 13. However, thematerial is not limited to a phase change recording material. Amagneto-optical recording material and a recordable type recordingmaterial such as a dye material can also be utilized.

More, a wavelength of a laser beam utilized for reproducing orrecording/reproducing is specified as 650 and 405 nm. However, awavelength is not limited to them. Any length such as 830, 635, 515,460, 430, and 370 nm, and their adjacent wavelength can be utilized.Moreover, with respect to a numerical aperture NA of a lens, any NA suchas 0.4, 0.45, 0.55, 0.65, 0.7, 0.75, 0.8, 0.85, and 0.9 other than 0.60can be applicable. In addition thereto, a lens having an NA of more than1.0, which is represented by a solid immersion lens, can also beapplicable.

According to an aspect of the present invention, as depicted above, theinformation recording medium, which comprises at least the read onlyarea 31 and the recording/reproducing area 32, can perform a traversereproduction over two areas by specifying push-pull signal outputs fromthe read only area 31 and the recording/reproducing area 32 to apredetermined range.

1-5. (canceled)
 6. An information recording medium comprising at least asubstrate and a recording layer, wherein said substrate is formed with aread only area and a recording/reproducing area, and wherein said readonly area and said recording/reproducing area do not overlap with eachother, and wherein a reflectivity of said recording layer is more than10%, and wherein said recording layer is formed continuously over atleast two areas of said read only area and said recording/reproducingarea, and wherein a push-pull signal output T1 reproduced from said readonly area is more than 0.1 and another push-pull signal output T2reproduced from said recording/reproducing area is more than 0.1, andwherein 1.5≧T1/T2≧0.5, and wherein said recording/reproducing area iscomposed of a groove and a land, and further wherein that track pitch ofsaid grooves is arranged so as to be 0.74 μm.
 7. An informationrecording medium comprising at least a substrate and a recording layer,wherein said substrate is formed with a read only area and arecording/reproducing area, and wherein said read only area and saidrecording/reproducing area do not overlap with each other, and wherein areflectivity of said recording layer is more than 10%, and wherein saidrecording layer is formed continuously over at least two areas of saidread only area and said recording/reproducing area, and wherein apush-pull signal output T1 reproduced from said read only area is morethan 0.1 and another push-pull signal output T2 reproduced from saidrecording/reproducing area is more than 0.1, and wherein 1.5≧T1/T2≧0.5,and wherein said recording layer is composed of a magneto-opticalrecording material.
 8. A reproducing method for reproducing aninformation recording medium comprising at least a substrate and arecording layer, wherein said substrate is formed with a read only areaand a recording/reproducing area, and wherein said read only area andsaid recording/reproducing area do not overlap with each other, andwherein a reflectivity of said recording layer is more than 10%, andwherein said recording layer is formed continuously over at least twoareas of said read only area and said recording/reproducing area, andwherein a push-pull signal output T1 reproduced from said read only areais more than 0.1 and another push-pull signal output T2 reproduced fromsaid recording/reproducing area is more than 0.1, and wherein saidrecording layer is composed of a recording material that is recordableby a wavelength of 405 nm, and further wherein the information recordingmedium is reproduced by irradiating a laser beam on said recording layerthrough a lens having a numerical aperture NA of any one selected outfrom 0.4 to 0.9.